The invention is based on a priority application EP 08305316.5 which is hereby incorporated by reference.
The invention relates to a method for allocation of parameters for radio transmission in a wireless communication network using channel feedback compression, wherein at least one channel impulse response in the time domain for at least one connection (CH13-CH24) between an antenna (A1, A2) of a transmitter (BS) and an antenna of a receiver (MS) is determined, only the at least one complex coefficient related to one or more time intervals of said at least one channel impulse response with a power higher than a predefined threshold is fed back, and parameters for radio transmission are allocated to said at least one connection (CH13-CH24) based on the at least one channel impulse response which is fed back.
A network element (MS) adapted to perform channel feedback compression for allocation of parameters for radio transmission in a wireless communication network, wherein the network element (MS) comprises at least one processing means adapted to determine the at least one channel impulse response in the time domain for at least one connection (CH13-CH24) between an antenna (A1, A2) of a further network element (BS) and an antenna (A3, A4) of said network element (MS), compare the power of said at least one channel impulse response with a predefined threshold, and transmit only the at least one complex coefficient related to one or more time intervals of said at least one channel impulse response with a power higher than said predefined threshold.
A network element (BS) adapted to perform allocation of parameters for radio transmission in a wireless communication network with channel feedback compression, wherein the network element (BS) comprises at least one processing means adapted to receive at least one complex coefficient related to one or more time intervals of at least one channel impulse response with a power higher than a predefined threshold for at least one connection (CH13-CH24) between an antenna (A3, A4) of said network element (BS) and an antenna (A1, A2) of a further network element (MS), and allocate parameters for radio transmission to said at least one connection (CH13-CH24) based on the at least one channel impulse response with a power higher than a predefined threshold.
A wireless communication network with at least one network element (MS) for determination of said one or more time intervals, said at least one channel impulse response is averaged over time or antenna links.
and at least one network element (BS) for allocation of parameters for radio transmission in a wireless communication network using channel feedback compression, wherein at least one channel impulse response in the time domain for at least one connection (CH13-CH24) between an antenna (A1, A2) of a transmitter (BS) and an antenna of a receiver (MS) is determined, only the at least one complex coefficient related to one or more time intervals of said at least one channel impulse response with a power higher than a predefined threshold is fed back, and parameters for radio transmission are allocated to said at least one connection (CH13-CH24) based on the at least one channel impulse response which is fed back.
In wireless communication systems like e.g. Third Generation Partnership Project Long Term Evolution (3GPP LTE) or Worldwide Interoperability for Microwave Access (WIMAX), the usage of antenna diversity that is applied e.g. in multiple-input multiple-output (MIMO) technology offers a high data rate achieved e.g. by means of a high spectral efficiency and diversity.
Orthogonal frequency division multiplexing (OFDM) can be used e.g. in broadband MIMO systems to divide frequency selective channels into a set of narrowband flat-fading subchannels. Such flat-fading subchannels can be used e.g. in a network that applies interference coordination in order to achieve a high data rate.
For the optimization of a MIMO-OFDM system, information about amplitude and phase of the different channels are needed at the transmitter side. Such information are typically fed back in form of channel state information (CSI) from a receiver to a transmitter. The channel state information (CSI) is required by nearly all MIMO algorithms at the transmitter side for allocation of parameters for radio transmission, as e.g. for choosing the appropriate antenna weights or modulation and coding schemes.
Due to frequency selectivity and temporal evolution of the channel on the one hand and the increased dimension by needing feedback for each transmitter antenna to receiver antenna link, this CSI feedback becomes very large, wasting uplink capacity for signaling load.
An approach according to the state of the art is to feed back for each pilot symbol a certain amount of bits, e.g. 16 bits, to obtain the complex coefficient of the channel transfer function for each channel. Thus, the amount of required feedback for this approach is extremely large.
Another standard approach is to transfer the channel into the time domain and feed back the channel impulse response (CIR). Again this gives a quite large overhead required for feedback.
According to other prior art solutions, temporal or frequency resolution or the granularity of the complex coefficients of the channel transfer function that are fed back is reduced. However, there will then be a loss in accuracy which may lead to a non-appropriate allocation of parameters for radio transmission.
A method for reducing feedback in a MIMO-OFDM network according to the prior art uses vector quantization compression to limit the size of feedback data required to be sent to a transmitter for optimizing communications between MIMO-OFDM devices. In finite state vector quantization feedback, optimal precoding matrices are selected sequentially across subcarriers. After selecting the first precoding matrix from a codebook of a certain size, subsequent preceding matrices are selected from a smaller time-varying codebook per subcarrier depending on prior decisions. Such a method for feedback reduction is e.g. described in the US patent application US 2007/0297529 A1.
However, this method reduces the feedback by means of reducing the size of the codebook per subcarrier and thus the needed amount of bits for feedback of the optimum precoding matrix instead of reducing the CSI feedback. If the MIMO algorithm that is used at the transmitter side needs CSI information in addition to information about the optimum precoding matrix, the huge amount of CSI feedback must be sent to the transmitter in addition to the information about the optimum precoding matrix.
So for all of the above mentioned approaches for channel feedback, it can be stated that either information is lost or the required feedback bandwidth is too high.
In order to have a high channel quality leading to a high data rate and at the same time enough uplink capacity for data transmission, reduction of the feedback of the channel state with low loss of significant information about the channel state is therefore required.